1. Field of the Invention
The technical scope of the invention is that of ammunition firing devices using a mechanical firing pin that impacts a pyrotechnic composition.
2. Description of the Related Art
Classically, firing devices incorporate a firing pin projected via inertia onto the pyrotechnic composition after a certain number of safety barriers have been raised. This firing pin is also very often projected by a spring, so as to ensure a self-destruct function (when, for example, there is no impact on a target).
Patent FR-2689972 thus discloses a firing device for a medium caliber projectile (caliber of between 20 mm and 50 mm). This device comprises a firing pin that can be pushed towards a primer by means of a spring.
So as to avoid any risk of inadvertent percussion during the storage or transport phases, the primer is integral with an arming rotor that enables it to be kept at a distance from the firing pin before firing.
Such architecture is, however, complicated and necessitates the manufacture of many mechanical parts incorporating precise machining.
Classically, the self-destruct spring is kept tensed during the storage and transport phases. Even if this spring is compressed slightly more during firing more often than not to enable the locks of the primer rotor to be removed, sufficient energy for self-destruction requires the storage of the spring in a tensed state.
The aim of the invention is to simplify such a device by proposing an architecture in which the percussive primer is still aligned with the firing pin but the shocks to which it is subjected during the storage and transport phases are not able to cause the percussion of the primer.
With the device according to the invention, only those stresses linked to firing can make the device able to be primed.
The invention also enables a self-destruct mechanism to be implemented in which the spring means do not need to be compressed during assembly.
Thus, thanks to the invention, the springs are not stored in their tensed state thereby ensuring the maintenance of the device's performances despite long storage phases and with substantial temperature ranges.
An ammunition firing device is also known by patent FR-1300100 that incorporates a firing pin integral with a percussion body that is locked in the safety position by balls.
This device thus incorporates a firing pin that is permanently aligned with the primer but which is locked by safety means that are removed for firing.
These safety means comprise two counterweights sliding through inertia, the first counterweight releasing the balls locking the firing pin.
This device is complicated in structure. It is, indeed, necessary for the two counterweights to slide in a predefined order for the firing pin to be released. Indeed, the balls are pushed by one of the counterweights against the second counterweight. It is thus necessary for the latter to be rapidly distance during firing to avoid the balls becoming blocked.
It is furthermore necessary for the second counterweight to remain locked (at least temporarily) to enable the locking balls to be ejected from the firing pin. This locking is ensured by other balls housed in a groove in the second counterweight, groove whose bottom is conical. These locking balls are thus moved away during firing by means of their axial inertia and thereafter engage against a ramp of the firing pin.
This solution, which is particularly costly with regard to machining and assembly, means that the spin rate of the projectile is no longer a factor. It is, however, not very reliable, the balls only remaining in the locking position because of the single action of the counterweight return spring.
Practically, upon impact on the target, it is classically the sole inertia of the firing pin (including that of the second counterweight) acting against the effect of a return spring, which ensures the ignition of the primer.
As all known solutions thus implement the inertia of a firing pin, the energy available on impact on a target is proportional to the mass of the firing pin and the distance over which the latter has travelled to ignite the primer. This energy E is equal to mγD, expression in which m is the mass of the firing pin, D its travel distance and γ the deceleration upon impact on a target.
Classically, geometries in which the firing pins are sliding rods that are not driven by springs, lead to relatively substantial strokes (of around ten millimeters).
The aim of the invention is to propose a device of simple design in which only those stresses linked to firing are able to make the device able to be primed, and furthermore in which the percussion function is completely disassociated from the energy supply function for percussion.
This enables the design of more compact percussion firing devices since it is no longer necessary for a substantial stroke to be provided for the firing pin.
The invention is more particularly applicable in the field of fuses and firing devices incorporating micro-machined or micro-engraved elements (MEMS—Micro Electro Mechanical System—technology).
For the past few years, all or part of safety devices for ammunition have been proposed to be manufactured using chips incorporating micro machined or micro engraved electro mechanical elements, either in an element deposited on a substrate or directly on the substrate itself. This technology known under the name of MEMS (Micro Electro Mechanical System) enables micro-mechanisms to be made by implementing a technique close to that used to make integrated electronic circuits.
Safety and arming devices are known, namely by patents EP1780495 and EP1780496, that implement a shutter to break the micro-machined or micro-engraved pyrotechnic train.
However, to date no firing device for ammunition is known with a mechanical firing pin that implements MEMS technology.
One of the reasons explaining this absence of solution is the impossibility of producing tensed-state springs using MEMS technology. It is thus necessary for these springs to be compressed in a storage position with all the ensuing difficulties of conducting such an operation with a device or very reduced dimensions (a MEMS chip generally has dimensions of less than or equal to 10 mm).